PVP blend under UV light irradiation

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 199 (2018) 220–227

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Photodegradation of methylene blue with PVA/PVP blend under UV light irradiation H.M. Zidan a, N.A. El-Ghamaz a, A.M. Abdelghany b, A.L. Waly c,⁎ a b c

Physics Department, Faculty of Science, Damietta University, New Damietta 34517, Egypt Spectroscopy Department, Physics Division, National Research Center, 33 El-Behouth St., Dokki, 12311 Cairo, Egypt Department of Basic Science, Higher Institute of Engineering and Technology, New Damietta, Egypt

a r t i c l e

i n f o

Article history: Received 6 August 2017 Received in revised form 15 March 2018 Accepted 23 March 2018 Available online 24 March 2018 Keywords: PVA/PVP blend Optical parameters Methylene blue Photodegradation

a b s t r a c t Homogenous films of PVA/PVP blend (1:1) doped with different levels of methylene blue dye (MB) were prepared using the casting technique. The absorption spectra of doped PVA/PVP blend showed two absorption peaks due to the chromophor groups of MB while the pure PVA/PVP blend does not. The UV irradiation causes photodegradation of MB dye. The recovery of photodegraded MB is observed after keeping the sample 3 h in atmospheric air. The value of the optical energy gap (Eg) decreases with increasing the doping levels with MB. The spectral distribution of absorption index (k) and refractive index (n) are determined from the reflection and transmission spectra in the spectral range 200–2500 nm. The dependence of both n and k on wavelength of the incident light and the wt% content of MB in PVA/PVP blend is discussed. A normal dispersion observed at wavelength λ N 370 nm for pure PVA/PVP blend and λ N 800 nm for MB doped samples. The obtained results suggest the possible use of the studied system in many applications. © 2018 Elsevier B.V. All rights reserved.

1. Introduction Polymers have attracted great attention of chemists and physicists all over the world, Because of their widespread applications in technological and scientific researches. These applications such as solar energy conversion, coatings, adhesives, lithography, light-emitting diodes, sensors, laser development and many probable applications in the future [1,2].The combination of polymeric materials with suitable additives gives complexes, which are useful in the development of advanced high-energy electrochemical devices such as fuel cells, batteries, and photo electrochemical cells with desirable sizes. Superior and desired properties of polymers can be achieved by doping them with many dopants [3,4]. In recent years dye doped polymers have special interest because of their electrical and optical properties, which can be modified to a specified requirement by doping process [5]. The importance of dyes doped polymers arises from their interesting properties, which are desired for potential application such as in optical storage devices, nonlinear optics, optical communication and information processing and holographic applications [6].One of the dyes is methylene blue (MB). MB is used recently in the field of pollutants and heavy metals removal from water resources [7,8]. Also, it is a sensitizer in photochemistry, especially in the areas of singlet oxygen production and reductive electron transfer.

⁎ Corresponding author. E-mail address: [email protected] (A.L. Waly).

https://doi.org/10.1016/j.saa.2018.03.057 1386-1425/© 2018 Elsevier B.V. All rights reserved.

Cristina et al. [9] reported that MB dye cannot be photobleached in a pure form, but in the presence of electron donor it become colorless (degraded) when irradiated. In order to bleach the MB dye, it must be imbedded into a suitable matrix as PVA, PMMA and dichromated gelatin. The degraded dye is the product of excitation of dye molecules due to irradiation and the electrons taken from the surrounding medium. The photodegradation of MB is studied when it doped in PVA solid matrix [10] and Gelatin matrix [11]. Yao et al. studied the photocatalytic degradation of MB under UVirradiation using TiO2 sol synthesized via a sol-gel method as a catalyst [12]. They reported that the performance of 92.3% for color removal was reached after 160 min. of UV irradiation. They also showed that the chromophor responsible for characteristic color of the MB were broken down and MB had been degraded. Several scientists studied the degradation process of MB in different media and conditions [13–16]. Poly vinyl alcohol (PVA) is very important polymeric materials due to its relatively low cost in manufacture in addition to its use in many applications in the industry. For example, phosphoric acid doped PVA is used as a solid polymer electrolyte in solid state photocells and solid state electro chromic display. Also, PVA as a semi crystalline material exhibits some physical properties resulting from crystal-amorphous interfacial effects [14]. Poly vinyl pyrrolidone (PVP) is a conjugated polymer has moderate electrical conductivity. Its importance arises from its easy processability and good environmental stability [17].

H.M. Zidan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 199 (2018) 220–227

Physical mixing (Blending) of polymers creates a new material with some of the desired properties of each individual polymer [18]. Blending is considered as an alternative to the high cost of developing new materials. It is known that the conducting polymers have been of limited usefulness in applications because of its instability and inprocessability. It has been possible to obtain a processable conductive blend by dispersing conducting polymer in a non – conducting polymer. PVP/ PVA blend have a good charge storage capacity and its electrical and optical properties strongly depend on the dopant [19]. The influence of PVP on crystallinity of PVA and optical band gap has been investigated by Saudha Kamath et al. [20]. They reported that the crystallinity of PVA/PVP blends decreases with increasing the level of PVP and PVA (50) wt%/PVP (50) wt% is more stable. In doping process, choosing the dopants is depending on their reactivity with the host polymer matrix [18–20]. On the other hand, the structural, optical, thermal and electrical properties of blends such as PVA/PVP blend can be suitably modified by the addition of a variety of dopants. Although some works have been reported on the doped polyblend of PVA/PVP films, very few experimental results are available on PVA/PVP doped with dye. In our previous study, we investigated the effect of MB dye doping level on the structural and electrical modifications of PVA/PVP films [21]. In this work, we continue our efforts to shed more light on the effect of these structural modifications on some optical parameters of this system. Also, we aimed to study the photodegradation of MB dye doped PVA/PVP matrix.

221

obtained films is in the range ~0.1–0.2 mm. The dopant level (wt%) was pre-calculated using Eq. (1): W ðwt%Þ ¼

Wd  100%; Wp þ Wd

ð1Þ

where Wp and Wd are the weight of polymer and dopant, respectively. 2.2. Physical Measurements Ultraviolet – Visible (UV–Vis) absorption spectra of the samples under test were carried out using a Perkin–Elmer UV–Vis spectrophotometer in the wavelength range 200–900 nm and at room temperature. Irradiation process was performed using a low pressure mercury lamp Cole Parmer (100 W) with monochromatic light of λ = 254 nm. The distance between samples and the lamp is kept at about 5 cm during irradiation process. The measurements of the transmittance, T(λ), and the reflectance, R(λ), of PVA/PVP films and MB doped PVA/PVP films were performed using a double-beam JASCO spectrophotometer model V-570 – UV–VIS-NIR at normal incidence of light and at room temperature in the wavelength range 200–2500 nm. The measured optical absorbance, transmittance and reflectance spectra are used to determine the optical constants such as refractive index n, absorption coefficient (α), optical energy gap, and the dielectric constant of the samples under test. 3. Results and Discussion 3.1. Absorption Spectra

2. Experimental 2.1. Materials and Sample Preparation The polyvinyl alcohol (PVA) used in this study was obtained from Merck-Germany with molecular weight 14,000, polyvinyl pyrrolidone (PVP) was obtained from Aldrish Chemical Co. USA with molecular weight 40,000 and Methylene blue (MB)was obtained from Mumbia-India. The molecular structure of PVA, PVP and MB are shown in Fig. 1. Equal weights of PVA and PVP (1:1) were dissolved in doubly distilled water at 50 °C with continuous stirring until complete miscibility. Methylene blue with different weight percentage (0%, 0.001%, 0.005%, 0.015%, 0.020% and 0.025%) added to the polymeric solution with continuous stirring for 2 h to ensure complete mixing. The samples were defined, as (D0.000–D0.025) where D0.000 is for pure samples and (D0.001–D0.025) are the doped samples with MB dye with different weight percentages 0.001%, 0.005%, 0.015%, 0.020%, 0.025% respectively. The blends with different MB dye levels were then casted in serialized Petri dishes. Prepared samples were dried in an incubator at 50 °C for 2 days. Dried samples peeled from Petri dishes and kept in a desiccators until use. The thickness of the

Optical absorption measurements have been proved to be very useful for elucidation of the electronic structure for crystalline and noncrystalline materials. The UV/Vis absorbance scan in the wavelength rang 200–900 nm of pure PVA/PVP blend and PVA/PVP blend doped with various doping levels of MB dye was recorded and shown in Fig. 2. The absorbance spectrum of the pure PVA/PVP blend demonstrates an absorption peak at 230 nm, which is attributed to the carbonyl groups along the polymer chain [22]. The doped samples with different doping levels of MB dye showed more two absorption peaks centered at about 290 and 630 nm in addition to the peak at 230 nm. It is reasonable to assign the observed new bands to the π-π* and n–π⁎respectively transitions of chromophoric groups in MB dye [23]. It is also observed that there is slight change in the band position with doping levels of MB dye. On the other hand, the increase of doping level increases the peaks intensity. This increase can be considered as an evidence for the incorporation of MB dye into the polymeric matrix. 3.2. Photo-degradation of MB In this section, we study the Photo-degradation of MB dye. The UV/ Vis spectra in the wavelength range 200–900 nm for pure PVA/PVP

Fig. 1. The molecular structure of (a) PVA, (b) PVP and (c) methylene blue (MB).

H.M. Zidan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 199 (2018) 220–227

3.5

230 nm

222

3.0

630 nm

1.5

UV-iradiation

0 min

0.6 0.5 Absorbance

2.0

290 nm

Absorbance

2.5

1.0

0.7

D0.000 D0.001 D0.005 D0.015 D0.020 D0.025

3 min

0.4 0.3

6 min 0.2

0.5

9 min 0.1

0.0 300

400

500

600

700

800

18 min

0.0

Wavelength λ (nm)

550

650

700

Wavelength λ (nm)

Fig. 2. UV/Vis scan for pure PVA/PVP blend films doped with different levels of MB.

blend (sample D0), pure MB dye and PVA/PVP doped with MB (sample D0.025) dye before and after UV-irradiation for different are shown in Fig. 3. The absorbance spectra for MB dye before and after UVirradiation are identical. It is also observed that the UV-irradiation has no effect on the absorbance spectrum of pure PVA/PVP blend. Therefore, PVA/PVP blend itself can be considered as a photo-stable polymer. On the other hand, for PVA/PVP blend doped with MB dye, the intensity of characteristic peaks of dye at 290 nm and 630 nm decreases upon UV-irradiation. These results confirm that the MB dye undergoes a photo-degradation in the presence of PVA/PVP blend as an electron doner medium [9]. We study in details the degradation process of MB dye and analyses the changes in absorbance of the main peak of MB (λ = 630 nm). The change of absorption spectra in the wavelength range 500–700 nm of MB doped PVA/PVP blend at dye level 0.025 wt% during UV- irradiation is shown in Fig. 4. From this figure, it is observed that a strong absorption region within the wavelength range 550–670 nm for the main absorption peak of MB dye. The absorption peak decreases gradually as the UV irradiation time increases. The peak position slightly red shifted. It is observed that the absorption peak disappeared completely after 18 min of irradiation. This result explains the visual observation of the change in color of original MB doped film upon UV-irradiation from blue to

600

Fig. 4. The absorbance spectra for PVA/PVP film doped with 0.025 wt% of MB after UVirradiation with different time.

transparent. This behavior can be interpreted on the basis of photoreduction of the colored MB dye molecules to leuco MB colorless [10]. Thus, based on the observation in Fig. 4, it would be concluded that the MB dye molecules embedded in PVA/PVP matrix exhibits an effective photo-bleaching process. The obtained experimental results suggest the MB doped PVA/PVP matrix to be used in some technological applications such as the waveguide manufacture and holographic recording system [24]. The photo-bleaching reaction mechanism of MB when embedded in PVA/PVP matrix can be summarized as follows [9,25]. (i) During UV-irradiation, the MB dye molecule is exited to the first excited state (1 MB*) where it can be changed to triplet excited state with a longer lifetime (3 MB*) as follow:

MB ðhνÞ→1MB →3MB

ð2Þ

(ii) The polymeric matrix (PVA/PVP blend) takes the role of the electron donor to bring MB to its leuco form (colorless) as: 4

D0 after UV- irradiation D0.025 before UV- irradiation D0.025 after UV- irradiation MB after UV- irradiation (deluted solution)

Absorbance

3

ð3Þ

It is also observed that the characteristic color of the MB dye doped PVA/PVP blend is recovered gradually after the colorless irradiated film is exposed to atmospheric air in the dark. This observation is confirmed by the recovery of the absorption peak at λ = 630 nm of the UV irradiated film after exposure to air for about 3 h as shown in Fig. 5. This phenomenon can be explained on the basis that Leuco form of MB dye molecules are re-oxidized when it in contact with atmospheric oxygen [24] as:

2

1

0 200

3MB þ PVA=PVP→intermediate product→leuco MB þ PVA=PVP blend

Leuco MB þ O2 →MB þ O2 300

400

500

Wavelength

600

700

ð4Þ

800

nm)

Fig. 3. Absorbance spectra for pure PVA/PVP film(D0.000), PVA/PVP blend doped with 0.025 wt% (D0.025) before and after UV-irradiation and UV-irradiated MB dye.

During gamma radiolysis of methylene blue in aqueous solutions, it has been demonstrated that methylene blue can be decolored and degraded by gamma radiolysis. The extent of dye destruction depends mainly on its concentration and radiation dose [25,26].

H.M. Zidan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 199 (2018) 220–227

180 min 0.6

dependence of the absorption coefficient near the absorption edge using the following frequency dependence of α [29]:

reverse


r αhv ¼ B hv−Eg ;

Absorbance

150 min 0.4 120 min 90 min

0.2

60 min 0.0 550

600

650

700

Wavelength λ (nm) Fig. 5. The recovery of absorbance peak at 630 nm after exposure to atmospheric air for PVA/PVP film doped with 0.025 wt% MB.

The existence of two phenyl groups only in this basic dye contributed much to its high sensitivity towards gamma radiation. The oxidized form of methylene blue (MBox) is blue, while the reduced form (MB red) is colorless. Oxidized form can be transformed to the reduced form and reactions involving the two forms of methylene blue are sometimes called clock reactions, because they involve a very sudden color change that is easy to time and 2e– oxidation of PVA was coupled with the 2e– reduction of methylene blue (MBox). The reduced form can be converted back to the oxidized form due to ordinary air (oxygen) atmosphere (see Scheme 1). 3.3. Optical Energy Gap It is known that a significant change have been observed in optical response of the polymers after doping or irradiation. The optical absorption spectra of a material can deduce information about the energy gap in crystalline and amorphous materials [27]. The absorption spectra for PVA/PVP blend and doped blends with different contents of the MB dye (Fig. 2) are characterized by a main absorption edge for all curves around λ ≈ 250 nm. The position of the main edge for the PVA/PVP blend is shifted to longer wavelength upon doping with different levels of MB dye. This shift can be considered as an indication of complexation between the MB dye and PVA/PVP blend. Also, may also be due to the change in crystallite size due to addition of the MB dye [28]. The absorption coefficient (α) can be calculated from the measured optical absorbance spectrum (Abs.) according to the following relation: α¼

2:303 Abs: ; X

223

ð5Þ

where X is the film thickness of the film. The optical band gap of MB doped PVA/PVP blend is calculated from the analysis of the spectral

ð6Þ

where B is a constant depends on the transition probability, hν is the energy of the incident photons, Eg is the value of the optical energy gap between the valence and the conduction bands, and r is the power which its value characterizes the transition process in the k- space and takes the values 1/2, 3/2, 2 and 3 for direct allowed, direct forbidden, indirect allowed and indirect forbidden transitions, respectively. The best fit of the experimental data was found for r = 2. This indicates that the optical transition of electrons is indirect in k- space and interactions with lattice vibrations (phonons) take place. From the plots of (αhν)1/2 versus hν near the fundamental absorption edge we can determine Eg. Fig. 6 represents the plot of (αhν)1/2 versus hν near the fundamental absorption edge for the films of pure PVA/PVP blend and PVA/PVP blend doped with different doping levels of MB dye. The values Eg are the intersection of the extrapolation of the linear region of the plots with the hν axis. The dependence of Eg on the doping level for the studied system is shown in Fig. 7. It is clear that the value of Eg for PVA/PVP blend decreases with increasing the doping levels. The change of Eg upon doping reflects the role of MB dye in modifying the electronic structure of the PVA/PVP blend. The addition of MB as a dopant may be the structural disorder in the polymeric matrix tend to increasing by increasing the MB doping level and consequently the appearance of various polaronic and defect levels takes place [30]. On the other hand, the density of localized state, N(E), in a polymeric matrix is proportional to the concentration of these defects. Consequently, the increase in MB dye content increases N(E) which is responsible of decreasing the gap between the conduction band and the valence band [31]. The absorbance spectra for PVA/PVP blend doped with different doping levels of MB dye (Fig. 2) show an extending tail for lower energies below the band edge. This tail can be attributed to the extended states in the band gap and was found to be related directly to the density of states corresponding to defect level in the forbidden gap. This tail is found to obey the empirical Urbach formula which given by [32].  α ðνÞ ¼ α o exp 

 hν ; ΔE

ð7Þ

where αo is a constant and ΔE is extension of the localized states in the band gap (Urbach energy). To verify Eq. (7), the values of ln α as a function of hν near the absorption edge for pure PVA/PVP film and doped films with different levels of MB dye are presented in Fig.8. The value of the Urbach energy (ΔE) is the reciprocal of the slope of the linear portion in the lower photon energy region of these curves. The calculated value of ΔE for pure PVA/PVP blend is 0.62 eV while the values of ΔE for PVA/PVP doped with MB dye are found to be in the range 0.62 and 0.70 eV. It was found that the value of ΔE for pure PVA/PVP blend is less than that of PVA/PVP doped samples. The increase of ΔE upon doping indicates an increase in disorder in doped ones.

Scheme 1. Oxidation and reduction of methylene blue.

224

H.M. Zidan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 199 (2018) 220–227

D0.000 D0.001 D0.005 D0.015 D0.020 D0.025

9

8

7

6

5 4.8

Fig. 6. Plots of (αhν)1/2 versus (hν) for pure PVA/PVP blend doped films with different contents of MB.

5.2

5.6

6.0

6.4

Fig. 8. The dependence of ln (α) for PVA/PVP blend doped with different levels of MB.

the refractive index (n) and the absorption index (k) and can be calculated using the following equations:

3.4. Reflection and Transmission Spectra The spectral behavior of absolute values of transmittance T(λ) and reflectance R(λ) for PVA/PVP blend doped with different doping levels of MB dye are measured at room temperature and normal incidence of light for the present system in the wavelength range 200–2500 nm and shown in Figs. 9 and 10, respectively. It is observed that the pure PVA/PVP blend film that T+R~1 at λ N 370 which indicates that the pure PVA/PVP blend is transparent in this region of spectra. On the other hand, the doped samples become transparent and no light is scattered or absorbed only at λ N 800 nm. The inequality T + R b 1 at λ b 800 nm is due to the presence of absorption peaks at 290 and 630 nm (see Fig. 2). The peaks are due to the presence of MB dye in the polymer matrix. This behavior obeys a multioscillator model [33]. The refractive index is an important parameter and it induces valuable information for the optical materials and is considered as a complex quantity. The complex refractive index n⁎ can be expressed as: n ¼ n−ik;

ð8Þ

where n and k are the real refractive index and the absorption index, respectively.

n¼

k¼

!1=2

4R

−k ð1−RÞ2

2

þ

  1þR 1−R

ð9Þ

αλ ; 4π

ð10Þ

where α can be calculated from T and R according to the relation: α¼

1 ln d

"

ð1−RÞ2 2T

! þ

ð1−RÞ4 4ðT Þ2

!#1=2 þ R2

ð11Þ

where d is the thickness of the film and λ is the wavelength of the incident light. From the previous equations, we can calculate the refractive index. Fig. 11 shows the spectral behavior of n for pure PVA/PVP blend and PVA/PVP blend doped with different contents of MB dye in the wavelength range 200–2500 nm. These spectra show that n of the pure blend decreases with increasing wavelength and reaches a nearly constant value at longer wavelength (normal dispersion), this behavior 0.96

4.90

0.88 D0.000 D0.001 D0.005 D0.015 D0.020 D0.025

0.80 Transmittance %

4.85

Eg (eV)

4.80

4.75

0.72 0.64 0.56 0.48 0.40 0.32 0.24 0.16

4.70

0.08 0.00 400

4.65 0

1E-3

0.005

0.015

0.02

0.025

800

1200

1600

2000

2400

Wavelength λ (nm)

Azo dye doping level (wt%) Fig. 7. The dependence of Eg on the doping level for the studied system.

Fig. 9. The spectral distribution of T(λ) for films of PVA/PVP and PVA/PVP doped with different levels of MB.

H.M. Zidan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 199 (2018) 220–227

0.16

0.12

D0.000 D0.001 D0.005 D0.015 D0.020 D0.025

-2

1.2x10

0.10 -3

9.0x10 0.08

k

Reflectance (R)

-2

1.5x10

D0.000 D0.001 D0.005 D0.015 D0.020 D0.025

0.14

225

0.06

-3

6.0x10

0.04 -3

3.0x10

0.02 0.00 400

800

1200

1600

2000

2400

0.0 200

Wavelength λ (nm)

300

400

500

600

700

800

Wavelength λ (nm) Fig. 10. The spectral distribution of R(λ) for films of PVA/PVP doped with different levels of MB.

is described by the single oscillator model. On the other hand, for the doped samples, the spectral behavior of n show normal dispersion behavior in the wavelength λ N 800 nm while they show anomalous dispersion at λ b 800 nm which can be explained in terms of the multioscillator model [33]. The variation of refractive index with doping can be attributed to the structural modifications occurred in the polymeric matrix due to the addition of MB dye. These results make us obtain any desired value of refractive index by using suitable doping level. Fig. 12 shows the spectral distribution of absorption index (k) for the studied system in the wavelength rang 200–2500 nm. The observed spectra show two absorption peaks at 290 and 630 nm for the doped samples, while the pure blend gives no any peaks. This behavior can be attributed to the presence a MB aggregations as a coloring centers.

Fig. 12. The spectral distribution of absorption index (k) for films of PVA/PVP and PVA/PVP doped with different levels of MB.

and ɛ i ¼ 2nk

ð14Þ

The spectral distribution of ɛr and ɛi for pure PVA/PVP blend and PVA/PVP blend doped with different levels of MB dye are shown in Figs. 13 and 14, respectively. It is shown that the values of ɛr and ɛi depend on the doping levels of MB dye due to structural modifications induced with the addition of MB dye. The obtained values of ɛr and the refractive index n in the nonabsorption region (λ N 800 nm) can also be analyzed in terms of a single oscillator model which can be expressed by the relation [34]:

3.5. Dispersion Analysis The permittivity (dielectric constant) of a material is a complex quantity which is directly related to the complex refractive index and it is a complex quantity too. It can be expressed by the following relation ε ¼ εr −iεi

ð12Þ

where ɛr is the real part and ɛi is the imaginary part of the complex permittivity. Both of ɛr and ɛi are related to n and k by the relations 2

εr ¼ n2 −k

εr ¼ εl −

e2 N λ2 ; 4πεo m c2

ð15Þ

where εo is the permittivity of free space,εl is the lattice dielectric constant, N/m⁎ is the carrier concentration to effective mass ratio, c is the speed of light and e is the electronic charge. Fig. 15 shows the plots of ɛr as a function of λ2 for the studied system. Linear fitting of these plots longer wavelength range the values of intersection with ɛr axes

ð13Þ 6 D0.000 D0.001 D0.005 D0.015 D0.020 D0.025

2.3 2.2 2.1 2.0

n

5 4

εr

1.9

D0.000 D0.001 D0.005 D0.015 D0.020 D0.025

3

1.8

2

1.7 1.6

1

1.5 1.4

0 0

500

1000

1500

2000

2500

λ,nm Fig. 11. The spectral behavior of refractive index (n) for PVA/PVP blend and doped with different contents of MB.

400

800

1200

1600

2000

2400

Wavelength λ (nm) Fig. 13. The spectral distribution of ɛr for films of PVA/PVP doped with different levels of MB.

226

H.M. Zidan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 199 (2018) 220–227 -2

6.0x10

Table 1 The calculated optical parameters for PVA /PVP doped with different levels of MB.

D0.000 D0.001 D0.005 D0.015 D0.020 D0.025

-2

εi

4.0x10

Sample name

D0.000

D0.001

D0.005

D0.015

D0.020

D0.025

Eo (eV) Ed (eV) εl N/m⁎ ∗ 1020 (kg−1·m−3) ε∞ Eg (eV)

0.7025 0.7550 2.88118 1.297 2.858 4.88

0.6389 0.2629 1.6248 7.612 1.610 4.83

0.6983 0.7343 2.7169 6.503 2.715 4.80

0.7543 0.6365 2.0629 5.5507 2.10 4.78

0.6166 0.5608 3.1645 3.992 3.154 4.74

0.6957 0.7008 2.9799 3.315 3.055 4.69

-2

2.0x10

0.0 400

800

1200

1600

2000

2400

Wavelength λ (nm)

4. Conclusions

Fig. 14. The spectral distribution of ɛi for films of PVA/PVP doped with different levels of MB.

and slope value. The value εl is the intersection. The ratio N/m⁎ can be calculated from the slope of the straight line according to relation: N 4πɛ o c2 ¼  slope m e2

ð16Þ

The calculated values of ɛl and N/m⁎ for PVA/PVP blend with different doping levels are presented in Table 1. Another approach for the analysis of the normal dispersion of the refractive index data in the nonabsorbing region is given by Wemple and Didomenico [35,36] in which the refractive index is related to the energy of the incident light by the relation: n2 −1 ¼

Eo E d 2

E2o −ðhνÞ

obtained from the intersection which equals to (ε∞ − 1)−1. The calculated values of, ɛ∞, Eo and Ed are listed in Table 1. It is clear that the value of ɛ∞ ɛl, Eo and Ed for doped films are greater than that of pure films. It is also observed that ɛl N ɛ∞ for doped films.

ð17Þ

where Ed and Eo are the dispersion energy and the single oscillator energy, respectively. To verify Eq. (17), plots of (n2–1)−1 versus (hν)2 for pure PVA/PVP blend and PVA/PVP blend doped with different levels of MB are presented and fitted to a straight line as shown in Fig. 16. The values of Eo and Ed are determined from the slope (=(EoEd)−1) of the straight line and its intersection (=Eo/Ed) with the vertical axis. The values of the high frequency dielectric constant ɛ∞ = n2∞ can be

Fig. 15. The plots of ɛr versus λ2 for films of PVA/PVP doped with different levels of MB.

In this study the results demonstrate significant modification in the optical properties in the pure PVA/PVP films due to doping it with MB dye. The following conclusions were drawn: 1- UV/VIS absorbance spectra show that the spectra of doped films contain two absorption peaks centered at λ = 290 and 630 nm assigned to the chromophoric groups of MB dye. 2- UV-irradiation has no effect on pure PVA/PVP blend and pure MB dye. On the other hand a photochemical reactions of the MB doped in PVA/PVP blend observed upon UV-irradiation. The photodegradation of MB was confirmed by a decrease of the absorption main peak of MB dye at 630 nm with increasing the irradiation time. 3- It is also observed that the photodegraded sample was recovered to its original color within 3 h after irradiation this occur because the leuco form of dye can return to the nonexcited state when it is contact with the molecular oxygen as reported by other researchers. 4- The analysis of the calculated values of Eg evidences the presence of induced energy states due to doping by MB dye. The transition is indirect in k – space and interactions with lattice vibrations (phonons) take place. It was noticed that Eg of pure blend is greater than that of the doped films and decreases with increasing the doping levels. The change of Eg upon doping may reflect the role of MB dye content in modifying the electronic structure of PVA/PVP blend. 5- The spectral distribution of both T(λ) and R(λ) in the wavelength range 200–2500 nm evidences the following: (a) The pure PVA/ PVP films are transparent and gives the normal dispersion region. On the other hand the doped films become transparent only at λ

Fig. 16. The plots of (n2 − 1)−1 versus (hν)2 for PVA/PVP doped with different levels of MB.

H.M. Zidan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 199 (2018) 220–227

N800 nm due to the presence of induced MB dye color centers in the polymer matrix. (b) The long wavelength refractive index (n∞) increases with increasing the doping level of MB dye. (c) Refractive index changes in the present suggests the applicability in optical devices. (d) The optical parameters of the samples such as εl, ɛ∞, N/m⁎, Eo and Ed have been evaluated. Reference [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]

M. Teroda, Y. Ohaba, J. Appl. Phys. 22 (1983) 1392. K. Shunichi, Radiat. Phys. Chem. 27 (1986) 65. H.M. Zidan, M. Abu-Elnader, Physica B 355 (2005) 308. H.M. Zidan, J. Polym. Sci. B Polym. Phys. 41 (2003) 112. H.M. Zidan, A. El-Khodary, I.A. El-Sayed, H.I. El-Bohy, J. Appl. Polym. Sci. 117 (2010) 1416. G.M. Pardeep, S. Cyriac, S. Ramkumar, C.S. Kaartha, Jpn. J. Appl. Phys. 39 (2000) 137–140. M. Ghaedi, A. Golestani Nasab, S. Khodadoust, M. Rajabi, S. Azizian, J. Ind. Eng. Chem. 20 (4) (2014) 2317–2324. M. Ghaedi, H. Mazaheri, S. Khodadoust, S. Hajati, M.K. Purkait, Spectrochim. Acta A Mol. Biomol. Spectrosc. 135 (2015) 479–490. S. Crystina, A.L. Roger, C.R. Pierre, Appl. Opt. 26 (1987) 1989. C.K. Sheng, W.M. Yunus, W.Z.W. Yunus, Z.A. Talib, M.M. Moksin, Solid State Sci. Technol. 11 (2003) 124. C.K. Sheng, W.M. Yunus, J. Pertanika, J. Sci. Technol. 13 (2005) 23. J. Yao, C. Wang, Int. J. Photoenergy (2010), https://doi.org/10.1155/2010/643182 Article ID 643182, 6 pages. G. Cano-Garcia, A. Martinez-Hernandez, J. Jimenez-Becerril, J. Chem. Soc. Pak. 34 (2012) 533.

227

[14] H. Safardoust-Hojaghan, M. Salavati-Niasari, J. Clean. Prod. 148( (2017) 31. [15] M. Hassanpour, H. Safardoust-Hojaghan, M. Salavati-Niasari, J. Mol. Liq. 229( (2017) 293. [16] A. Abbasi, M. Hamadanian, M. Salavati-Niasari, S. Mortazavi-Derazkola, J. Colloid Interface Sci. 500( (2017) 284. [17] I.S. Elashmawi, H.E.A. Baieth, Curr. Appl. Phys. 12 (2012) 141. [18] C.V.S. Reddy, X. Han, Q.Y. Zhu, L.Q. Mai, W. Chen, Microelectron. Eng. 83 (2006) 281. [19] H.M. Ragab, Physica B 406 (2011) 3759–3767. [20] M.K. Sudha Kamath, H.G. Harish Kumar, R. Chandramani, M.C. Radhakrishna, Arch. Phys. Res. 6 (2) (2015) 18–21. [21] H.M. Zidan, N.A. Elghamaz, A.M. Abdelghany, A. Lotfy, Int. J. Electrochem. Sci. 11 (2016) 9041–9056. [22] H.M. Zidan, Polym. Test. 18 (1999) 449. [23] A.K. Srivastava, H.S. Virk, J. Polym. Mater. 17 (2000) 325. [24] C. Nadia, A.L. Roger, Appl. Opt. 27 (1988) 3008–3012. [25] Abbass ElZin, PhD thesis Self-healing Clay-Polymer Mixtures: Towards a New Material, School of Civil Engineering at the University of Sydney2013. [26] P. Zhang, F.Y. Deng, Y. Peng, H.B. Chen, Y. Gao, H.M. Li, RSC Adv. 4 (2014) 47361. [27] C. Nadia, A.L. Roger, Appl. Opt. 30 (1991) 1196–1200. [28] R. Mishra, S.P. Tripathy, D. Sinha, K.K. Dwivedi, S. Ghosh, D.T. Khating, M. Muller, D. Fink, W.H. Chung, Nucl. Instr. Meth. B 168 (2000) 59. [29] E.M. Abdelrazek, I.S. Elashmawi, Polym. Compos. 2 (9) (2008) 1036. [30] J. Tauc, Amorphous and Liquid Semiconductors, Plenum Press, New York, 1974 159. [31] N.F. Mott, Philos. Mag. 24 (1970) 1. [32] F. Urbach, Phys. Rev. 92 (1953) 1324. [33] A. Stendal, U. Beckars, S. Wilbrand, O. Stenzel, C. Von Borezys-Kowski, J. Phys. B Atomic Mol. Phys. 29 (1996) 2589. [34] J.N. Zemel, J.D. Jensen, R.B. Schoolar, Phys. Rev. A (140) (1965) 330. [35] M. Didomencio, S.H. Wimple, J. Appl. Phys. 40 (1969) 720. [36] S.H. Wemple, M. Didomencio, Phys. Rev. B Condens. Matter 3 (1971) 1338.